The role of Arabidopsis AtFes1A in cytosolic Hsp70 stability and abiotic stress tolerance.

AtFes1A is induced by high temperatures, and encodes a protein containing the armadillo repeat motif. Little is known about its biological function, however. In this study, we observed an increased heat-sensitive phenotype in atfes1a mutants, suggesting the involvement of AtFes1A in acquired thermotolerance. We found that AtFes1A is cytosolic and associates with cytosolic Hsp70. Loss of AtFes1A leads to a selective reduction of cytosolic Hsp70 and a global increase in heat shock transcription. Thus, AtFes1A appears to prevent cytosolic Hsp70 degradation, and acts as a negative regulator of heat-shock transcription. We also found increased ubiquitination of total protein in atfes1a mutants after severe heat stress. These findings suggest that AtFes1A plays an important role in heat response signalling pathways, in addition to its role in thermotolerance.